164 patients with mild-to-moderate knee osteoarthritis were randomized to a combined glucosamine sulfate and chondroitin sulfate (GS/CS) daily treatment or a placebo for 6 months. The purpose of this study was to compare pain reduction and functional improvement between groups after 6 months. Results demonstrated a significantly greater visual analog scale (VAS) pain reduction in the placebo group compared to the GS/CS group after 6 months, and non-significant differences between groups for improvement in Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) scores or OMERACT-OARSI response rate.